With development of communications technologies, more data is transmitted in a wireless communications system. To meet user requirements, higher transmission efficiency and a higher throughput are needed. Therefore, how to improve resource utilization and data transmission efficiency of limited time-frequency resources becomes a key problem. Cell resources are reused in a D2D ProSe (Device to Device Proximity Service, device to device proximity service). Therefore, terminal devices can perform direct communication, thereby improving resource utilization and network capacity.
In the prior art, for example, in a D2D scenario of an LTE (Long Term Evolution, Long Term Evolution) system, terminal devices such as mobile phones and tablet computers perform direct communication in a D2D system. Therefore, the devices have relatively great mobility, and channel states change relatively quickly. If a distance between the two terminal devices performing direct communication is relatively long or channel quality changes relatively greatly, the two terminal devices cannot perform. D2D communication,